(Not Applicable)
The present invention generally relates to alignment systems and techniques, and in particular to a streamlined method and apparatus for aligning a sensor to an aircraft using the inertial frame reference of the aircraft.
Sensors may typically comprise a camera, radar or laser radar, or navigational equipment, or any other related type of equipment. As a general rule, sensors are calibrated to their host aircraft""s inertial frame reference by first stabilizing the aircraft (i.e., shoring up the aircraft) and then bore sighting the sensor to precisely align it with the aircraft prior to being fixed in place. This is a cumbersome and time consuming technique and must be done for each sensor attached to each aircraft during the installation process.
A prior art approach is to add a three-axis inertial measurement unit to the sensor to compare with three-axis inertial measurements from the host aircraft. This adds cost and weight to the sensor, and requires the aircraft to fly for a period of time with the sensor to gather sufficient inertial measurements to determine the relative alignment between them.
An exemplary prior art device for measuring changes in the alignment of a component with respect to a reference axis of an aircraft is disclosed in U.S. Pat. No. 4,168,123, entitled AIRCRAFT WEAPONS SYSTEMS. This prior art device measures alignment by measuring displacement through a lens apparatus remote from the source. The device employs an infrared or electromagnetic source located on a wing-mounted pod of an aircraft with a lens focusing apparatus that focuses on targets mounted on the fuselage of the aircraft. Any measured displacement is provided in the form of an output signal indicative of the displacement. The output signal is then used by the aircraft""s weapons system to take into account such displacement.
On the other hand, the invention disclosed in this application employs a laser or other light source collocated with a target/sensor, which measures misalignment by measuring displacement of a laser, light or other beam reflected off of a pair of simple mirrors. The mirrors are permanently attached to and aligned with the inertial frame reference of the host aircraft. It should be noted that with the invention disclosed herein a single beam is used to measure two angles of alignment (e.g., pitch and yaw), whereas the above-referenced patented device requires two beams to measure a single angle of alignment (e.g., pitch).
Another similar prior art device for measuring changes in the alignment of a component with respect to a reference axis of an aircraft is disclosed in U.S. Pat. No. 3,633,212, entitled SYSTEM FOR DETERMINING THE ORIENTATION OF AN OBJECT BY EMPLOYING PLANE POLARIZED LIGHT. This prior art device employs a polarized light source and a motion picture camera, both of which are mounted on the aircraft. It is noted that the light source and the camera are not collocated, but are located some distance apart from one another. A plurality of specially oriented light-polarizing reflectors are attached to the component (e.g., a missile), which are observed by the camera. A source of plane-polarized light on the aircraft illuminates the reflectors on the missile. The attitude of the latter with respect to this source determines the amount of illumination picked up by the camera from each reflector. Such data is then coordinated to yield the positional information desired.
In contrast to the prior art device just described, the present invention measures alignment directly by measuring displacement of a laser, light or other beam reflected off of a pair of simple mirrors that are aligned with the inertial frame reference of the aircraft.
There is a need for an improved, low-cost technique for aligning a sensor with a host aircraft that will be easier and faster while maintaining the same degree of accuracy.
Accordingly, a feature of the present invention is the provision of an improved technique for calibrating any misalignment of a sensor attached to an aircraft with the aircraft""s inertial frame reference.
Another feature of the present invention is the provision of an alignment detection mechanism and technique that can be quickly read and interpreted and may be used by the host aircraft""s on-board computer in compensating for any deviation in alignment.
Yet another feature of the present invention is the use of low-power lasers and mirrors to read and interpret any misalignment between a host aircraft""s inertial frame reference and the frame reference of an attached sensor.
An advantage of the present invention over the prior art devices is that the number of components are greatly decreased, thereby reducing the cost and simplifying the device.
Another advantage of the present invention is the elimination of measurement errors due to position and lateral displacement uncertainties from the source, target/sensor, or store object being measured.
Still another advantage of the present invention is that, by collocating the source and target, the design and system operation is simplified.
These and other features and advantages, which will become apparent as the invention is described in detail below, are provided by an apparatus for sensing misalignment between an aircraft""s inertial reference frame and a reference frame of an attached sensor. The apparatus includes a first laser mounted on the sensor and in the center of and normal to a first measuring surface aligned with the frame reference of the sensor; and, a second laser also mounted on the sensor perpendicular to the first laser and in the center of and normal to a second measuring surface also aligned with the frame reference of the sensor. A first reflector is mounted to and aligned with the inertial reference frame of the aircraft and is disposed for reflecting a beam of light from the first laser, whereby misalignment in roll and yaw between the sensor pod and the aircraft is reflected on the first measuring surface. In a similar manner, a second reflector is mounted and aligned with the inertial reference frame of the aircraft and perpendicular to the first reflector, and is disposed for reflecting a beam of light from the second laser, whereby misalignment in roll and pitch between the sensor pod and the aircraft is reflected on the second measuring surface. The misalignment bias may later be read manually or electronically, and then used by the aircraft computer system to compensate for the bias.
Moreover, a method is disclosed for sensing misalignment between an aircraft""s inertial reference frame and a reference frame of an attached sensor. The method includes the steps of emitting a first light beam from and normal to a first measuring surface mounted on the sensor, wherein the first measuring surface is aligned with the reference frame of the sensor. Next, a second light beam is emitted from and normal to a second measuring surface mounted on the sensor, wherein the second measuring surface is also aligned with the reference frame of the sensor. After this, the first light beam is reflected from a reflector mounted on and aligned with an inertial reference frame of the aircraft, whereby misalignment in roll and yaw between the sensor and the aircraft is reflected on the first measuring surface. In a similar manner, the second light beam is reflected from a reflector mounted perpendicular to the first reflector and aligned with the inertial reference frame of the aircraft, whereby misalignment in pitch and roll between the sensor and the aircraft is reflected on the second measuring surface. The misalignment bias may later be read manually or electronically, and then used by the aircraft computer system to compensate for the bias.
Still other features and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein is shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive, and what is intended to be protected by Letters Patent is set forth in the appended claims.